1. Field of the Invention
This invention relates to methods and apparatuses for inspection and modification of intervertebral disc tissue and more particularly to the diagnosis and treatment of intervertebral disc problems using percutaneous disc techniques without the need for major surgical intervention.
2. Description of Related Art
Intervertebral disc abnormalities have a high incidence in the population and may result in pain and discomfort if they impinge on or irritate nerves. Disc abnormalities may be the result of trauma, repetitive use, metabolic disorders and the aging process and include such disorders but are not limited to (i) localized tear or fissure in the annulus fibrosus, (ii) localized disc herniations with contained or escaped extrusions, and (iii) chronic, circumferential bulging discs.
Disc fissures occur result from structural degeneration (a part of the aging process that may be accelerated by trauma) of fibrous components of the annulus fibrosus. Sneezing, bending or just attrition can separate these degenerated annulus fibers, creating a fissure. The fissure may or may not be accompanied by extrusion of nucleus pulposus material into or beyond the annulus fibrosus. The fissure itself may be the sole morphological change, above and beyond the generalized degenerative changes in the connective tissue of the disc. Due the fissure, biochemicals may escape from the disc and irritate surrounding structures. Disc fissures can be debilitatingly painful. The fissure may also be associated with a herniation of that portion of the wall.
With a contained disc herniation, the nucleus pulposus may work its way partly through the annulus and there are no free disc fragments in the spinal canal. Nevertheless, this is problematic because the outward protrusion can press on the spinal nerves or irritate other structures.
Another disc problem occurs when the disc bulges out circumferentially in all directions and not just in one location. This occurs when over time, the disc weakens, bulges and takes on a "roll" shape. Mechanical stiffness of the joint is reduced and the joint may become unstable. One vertebra may eventually settle on top of another. This problem continues as the body ages and accounts for shortened stature in old age. With the increasing life expectancy of the population, such degenerative disc disease and impairment of nerve function are becoming major public health problems. As the disc "roll" extends beyond the normal circumference, the disc height may be compromised, foramina with nerve roots are compressed. In addition, osteophytes may form on the outer surface of the disc roll and further encroach upon the spinal canal and for the nerve foramina. This condition is called lumbar spondylosis.
It has been thought that disc degeneration creates pain predominantly via segmental instability which disturbs sensitive structures which register pain. Traditional, conservative methods of treatment include bed rest, pain and muscle relaxant medication, physical therapy or steroid injection. Upon failure of conservative therapy, spinal pain (assumed to be due to instability) has been treated by spinal fusion, with or without instrumentation, which causes the vertebrae above and below the disc to grow solidly together and form a single, solid piece of bone. The procedure is carried out with or without discectomy. Other treatments include discectomy alone or disc decompression with or without fusion. Other methods include laminectomy or percutaneous nuclectomy to reduce pressure on the annulus by removing some of the interior nucleus pulposus. Surgical complications include disc space infection, nerve root injury, hematoma formation, instability of the adjacent vertebrae and collapse of the disc from further decrease in height.
These interventions have been problematic in that alleviation of back pain is unpredictable even if surgery appears successful. In attempts to overcome these difficulties, new devices have been introduced to the market, including but not limited to pedicle screws and interbody fusion cages. Although pedicle screws provide a high fusion success rate, there is still no direct correlation between fusion success rate and patient improvement in function and pain. Studies on fusion have demonstrated success rates of between 50% and 67% for pain improvement, and a significant number of patients have more pain postoperatively. Therefore, different methods of helping patients with degenerative disc problems need to be explored.
FIGS. 1(a) and 1(b) illustrate a cross-sectional anatomical view of a vertebra and associated disc and a lateral view of a portion of a lumbar and thoracic spine, respectively. Structures of a typical cervical vertebra (superior aspect) are shown in FIG. 1(a): 104--lamina; 106--spinal cord; 108--dorsal root of spinal nerve; 114--ventral root of spinal nerve; 116--posterior longitudinal ligament; 118--intervertebral disc; 120--nucleus pulposus; 122--annulus fibrosus; 124--anterior longitudinal ligament; 126--vertebral body; 128--pedicle; 130--vertebral artery; 132--vertebral veins; 134--superior articular facet; 136--posterior lateral portion of the annulus; 138--posterior medial portion of the annulus; and 142--spinous process. FIG. 1(b) is a lateral aspect of the lower portion of a typical spinal column showing the entire lumbar region and part of the thoracic region and displaying the following structures: 118--intervertebral disc; 126--vertebral body; 142--spinous process; 170--inferior vertebral notch; 110--spinal nerve; 174--superior articular process; 176--lumbar curvature; and 180--sacrum.
The presence of the spinal cord and the posterior portion of the vertebral body, including the spinous process, and superior and inferior articular processes, prohibit introduction of a needle or trocar from a directly posterior position. This is important because the posterior disc wall is the site of symptomatic annulus fissures and disc herniations and protrusions/extrusions that compress or irritate spinal nerves for most degenerative disc syndromes. The inferior articular process 168, along with the pedicle 128 and the lumbar spinal nerve 110, form a small "triangular" window (shown in black in FIG. 1(c)) through which introduction can be achieved from the posterior lateral position. FIG. 1(d) is a cross-sectional view of the lower back with an instrument introduced by the posterior lateral approach.
It is well known to those skilled in the art that percutaneous access to the disc is achieved by placing an introducer into the disc from this posterior lateral approach, but the triangular window does not allow much room to maneuver. Once the introducer pierces the tough annulus fibrosus, the introducer is fixed at two points along its length and has very little freedom of movement. Thus, this approach has allowed access only to small portions of the central and anterior nucleus pulposus. Current methods do not permit percutaneous access to the posterior half of the nucleus or to the posterior wall of the disc. Major and potentially dangerous surgery would be required to access these areas.
U.S. Pat. No. 5,433,739 (the "'739 patent") discloses placement of an RF electrode in an interior region of the disc approximately at the center of the disc. RF power is applied, and heat then putatively spreads out globally throughout the disc. The '739 patent teaches the use of a rigid shaft which includes a sharpened distal end that penetrates through the annulus fibrosus and into the nucleus pulposus. In one embodiment the shaft has to be rigid enough to permit the distal end of the RF electrode to pierce the annulus fibrosus, and the ability to maneuver its distal end within the nucleus pulposus is limited. In another embodiment, a somewhat more flexible shaft is disclosed. However, the embodiments of the '739 patent do not permit access to the posterior, posterior lateral and posterior medial region of the disc; nor do they provide for delivery of material to treat the annulus, nor do the embodiments permit temperature monitoring at the posterior annulus.
U.S. Pat. No. 5,201,729 (the "'729 patent") discloses the use of an optical fiber that is introduced into a nucleus pulposus. In the '729 patent, the distal end of a stiff optical fiber shaft extends in a lateral direction relative to a longitudinal axis of an introducer. This prevents delivery of coherent energy into the nucleus pulposus in the direction of the longitudinal axis of the introducer. Due to the limited access from the posterior lateral approach, stiff shaft and lateral energy deliver, the device of the '729 patent is unable to gain close proximity to a selected portion of the annulus (i.e., posterior, posterior medial and central posterior) requiring treatment or to precisely control the temperature at the annulus. This patent also does not teach injecting materials into the disc.
Accordingly, it is desirable to diagnose and treat disc abnormalities at locations previously not accessible via percutaneous approaches without substantial destruction to the disc. It would further be desirable to be able to administer materials to a precise, selected location within the disc, even at the posterior, posterior lateral and the posterior medial regions of the inner wall of the annulus fibrosus.